The invention relates to an apparatus for transporting a continuous elongate material web along a production line or the like where the material web is subjected to various processing operations which lead to a final product. The direction of transport of the material web corresponds to the longitudinal extension of the web.
In the manufacture of products produced from a continuous elongate material web where each product item is made on or from a discrete length of the web, problems arise in terms of production capacity in the machines in which the maximum machine or transport speed is limited due to the time required to perform an intermittent processing step or operation on the product to be formed on or from the material web. For example, in the manufacture of absorbent articles, such as baby diapers, sanitary napkins, incontinence pads and the like made up of layers of absorbent, liquid permeable and liquid impermeable material, various processing steps such as gluing, ultrasonic welding, fast mechanical processing etc. are required to be intermittently or periodically performed along the whole or less than the whole length of each product. Such processing operations or any other operations to be formed on any kind of product produced on or from an elongate material web or webs moving at a continuous speed past the processing station can result in an overall reduction in productivity because the intermittently or periodically performed processing step cannot be performed at the same speed as another processes to be carried out on the product. Therefore, the slowest processing step determines the maximum machine speed.
An apparatus for transporting an elongate flexible object such as a web wherein the speed of a section of the web is periodically varied while maintaining a constant speed of the upstream and downstream sections of the web is known from WO 95/12491 and WO 95/12539. In this known apparatus, the elongate web is continuously fed past rotating transport rollers which are oscillated parallel to the web in the direction of transport and opposite to the direction of transport thereof. During oscillation, three lengths of the elongate web are mutually parallel to each other so that a length of the web has a relative velocity which can be increased, reduced or reversed with respect to a stationary point by the oscillation of the transport rollers. This permits the performance of a processing operation on the web at a different speed than the constant speed of the web at the upstream and downstream sections of the apparatus. However, the known apparatus is relatively complicated in design and has relatively large moving masses. Additionally, the oscillating motion involves abrupt changes in direction, creating large forces which the apparatus must be designed to withstand.
It is therefore an object of the present invention to provide an apparatus for transporting a continuous elongate material web which is relatively simple in design but simultaneously makes it possible to easily adapt to different operating conditions.
This object is solved by an apparatus for transporting a continuous elongate material web according to the present invention.
The inventive apparatus comprises transport means arranged to transport the material web at a constant speed between a most upstream position and a most downstream position as seen along the path of transport of the material web, and at least two material web guide means arranged between the most upstream and most downstream positions along the transport path, at least one guide means being arranged upstream and at least one guide means being arranged downstream of an intermediate position between the most upstream and most downstream positions. The upstream and downstream guide means are movable relative to each other so as to impart a sinusoidal variation in speed to the material web at the intermediate position. In particular, each guide means is eccentrically rotatably mounted so as to move substantially continuously between a position in which a maximum partial length of the material web and a position in which a minimum partial length of the material web is temporarily supported by the guide means. Further, the upstream guide means moves at the same speed and in the opposite sense to the downstream guide means such that the length of the material web between the most upstream position and the most downstream position is substantially constant.
In accordance with the inventive apparatus, the production capacity is advantageously increased on account of the possibility of increasing as a whole the running or transport speed of the continuous flexible elongate material web through the apparatus while still being able to periodically or intermittently perform a processing step or operation which could not otherwise be performed at the higher constant speed of the web upstream and downstream of the inventive apparatus. This is because the inventive apparatus produces with a very simple structure a superimposed sinusoidal-like variation in velocity, i.e. relative speed of the material web with respect to a fixed point at an intermediate position along the transport path of the material through the inventive apparatus. Consequently, as compared to the constant speed, there is a change in speed of zero, increasing speed, zero, decreasing speed and back to zero at the intermediate position. By adding the sinusoidal-like variation to the constant or normal running speed by means of the inventive apparatus, the velocity through the apparatus gently changes between a value lower than the constant speed and a value higher than the constant speed. Thus, a processing step to be periodically or intermittently carried out on the material web and which requires more time than would be available at the constant speed at which the material web moves along the production line, can be performed during the low velocity period without the overall constant speed being influenced by the slower processing step. It is even possible to reduce the velocity or speed to zero if the process step requires this. Naturally, the apparatus of the present invention is suitable for implementation in a production line in which, when the products are formed along the material web without an intermediate gap between each product, only part of the length of each product along the material web is to be processed in the intermittent or periodic processing step, or, when there is a gap of an appropriately selected length, the whole length of the product can be processed. This is because the low velocity or speed period must be compensated by a high velocity or speed period of the same magnitude so as to maintain the same overall constant speed of the production line, and this compensation requires an unprocessed length along the material web.
Advantageously, the present invention can be realized in any production line requiring a relatively slow intermittent processing step. Such a slow step does not place a limitation on productivity and economy, as an overall higher line capacity can be achieved. Further, an existing production line which up to now has been limited in speed due to a slow processing step can be converted to run at a higher speed with an apparatus according to the present invention provided for the slow processing step.
An important and significant advantage of the inventive apparatus results from the fact that all main rotary parts thereof are rotated at a constant speed so that they must not be periodically accelerated. Therefore, the machine can be simpler in design and does not need to be constructed to absorb sudden increases in force caused by the periodic acceleration of masses as a result of any abrupt change in direction. The running speed of the inventive apparatus is hardly limited since the sinusoidal-like variation in speed is gentle and smooth and large masses do not have to be moved.
A particularly favourable embodiment of the inventive apparatus comprises a pair of upstream guide means and a pair of downstream guide means, each guide means being eccentrically rotatably mounted about a fixed axis of rotation. Further, the two guide means of a respective pair are rotatable in the same direction or opposite directions such as to define a maximum and a minimum distance therebetween. This arrangement provides a relatively simple but stable mechanism by means of which the sinusoidal-like variation in speed of the material web through the apparatus is achieved in a very smooth and gentle manner with no abrupt changes in direction and the resulting undesirable accelerating masses and the forces these produce. All of the guide means are rotated at the same speed and make one revolution per product along the material web so that a slow intermittent processing step can be performed on each product during the low velocity period of the material web. The distance between the respective pairs of guide means in the inventive apparatus can be freely selected such as to create a smaller or larger free length which provides the low velocity period within which the desired slow processing step can be performed. Additionally, it is possible to perform the process on the whole product or several products at the same time so long as the intermittent process is limited to part of the cycle time for one product produced on or from the material web. Additionally, the distance between the rotating centers in each pair of guide means which creates the length variation for each cycle does not strictly depend on the product length. However, the length of material web taken up in a respective pair effects the amplitude of the sinusoidal-like curve of speed variation. A smaller amplitude provides a relatively longer period of time during which the speed of the material web in the inventive apparatus is lowest so as to perform the slow intermittent processing step. Therefore, a relatively flat sinusoidal-like curve with a low amplitude is preferable for performing the intermediate processing step because there is a shorter low velocity period when the speed variation has a larger amplitude.
At least one and preferably all of the inventive guide means comprise an eccentrically mounted drum, shaft or the like about the periphery of which the material web is guided. The peripheral surface is suitably formed or coated or rotatable about its axis of rotation so as to present as little resistance as possible to the material web which is guided by it. This reduces any tensional forces which may be exerted on the material web while it passes through the inventive apparatus. Further, the drum, shaft or the like is advantageously counterbalanced for smoother operation of the inventive apparatus.
According to another preferred embodiment of the invention, at least one upstream and/or at least one downstream guide means are each provided with a compensating means arranged to coact with the associated guide means so as to prevent any slack in the material web along the transport path. This may be necessary, for example, if the material web is flexible and has become slightly elongated during processing. The compensating means can be an eccentrically mounted shaft or the like. Additionally, the compensation means can be used to take up any small difference in length of the material web at the respective guide means if such is present on account of the particular arrangement of the respective guide means.
In accordance with the invention, a material web processing means is provided at the intermediate position and arranged to process the material web periodically or intermittently when the speed of the material web at the intermediate position is at the lower speed period of the sinusoidal-like variation in speed. Advantageously, the processing means can also be movable relative to the material web in the direction of transport of the material web and in the same periodic cycle as the movement of the upstream and downstream guide means. If desired, this arrangement can be used to enhance the effect of the guide means such that the relative speed between the processing means and the material web is low or even zero or almost zero so as to further increase the time within which a relatively slow processing step can be performed by the processing means. Alternatively, the processing means can be movable at a speed which is just enough to reduce the relative speed as compared to the material web so as to follow the moving web and still be able to satisfactorily perform the processing step. In accordance with the present invention, the term processing means should be construed to cover means which perform one or more than one individual processing operation during the processing step.
If necessary, a support means can be provided on the opposite side of the material web to the processing means to support the material web during the processing step. The support means suitably comprises a drum or the like which is rotatable in the direction of transport of the material web and advantageously has a material web support surface which permits relative movement between the drum and the material web. For example, the support surface can be formed by a series of rotatable shafts or the like having rotational axes extending transversely to the direction of transport of the material web. Alternatively, the support surface can be formed of a low friction material. Such a support surface enhances the processing operation with the processing means when there is relative motion between the material web and the processing means and, in particular, when the processing step involves contact of the processing means with the material web.
It is also of advantage in accordance with the inventive apparatus that the support surface of the support means has a pattern formed thereon which is adapted to the shape of the material web or product to be processed. The processing means may also have such a suitably adapted surface if required. In particular, the pattern may consist of grooves, recesses or molds which enhance the positioning of the material web or the product to be formed on or from the material web with respect to the processing means so as to ensure proper alignment for the processing step. This is especially advantageous in the case of relative movement between the material web and the processing means.
According to another advantageous embodiment, the inventive apparatus further comprises at least one conveyor belt movable in the direction of transport of the material web in contact with one side thereof at least between a position upstream of the upstream guide means and a position downstream of the downstream guide means along the transport path. Such a conveyor belt can be used to hold material of or on the material web to prevent it from falling off the material web or to prevent the material web from slipping or being displaced during movement along the transport path and especially during the periods of high velocity or acceleration.
A particularly advantageous further embodiment comprises an apparatus for transporting first and second continuous elongate material webs relative to each other, said apparatus comprising an apparatus for transporting the first material web having transport means and guide means in accordance with the invention as described above such that a sinusoidal-like variation speed of the first material web is produced, and a second transport means arranged to transport the second material web along a path of transport of the second material web separate from the path of transport of the first material web. The second material web transport path crosses the first material web transport path at the intermediate position between the upstream and downstream guide means of the first material web and these guide means are arranged at an angle to the direction of transport of the first material web such that the first material web is guided so as to periodically have a component of movement in the same direction as the direction of transport of the second material web.
This apparatus is particularly advantageous for use in a production line in which an element produced longitudinally along the transport path of the second material web is to be mounted on the product produced along the transport path of the first material web such that it extents at an angle or transversely across the direction of transport of the first material web. Thus, for example, an element of the final product which can be easily produced in the longitudinal running direction of the second material web and must be mounted transversely can be attached under full control to the first material web without having to turn the element by 90xc2x0, which would require relatively complicated machinery and could otherwise represent a limitation in respect of the speed at which the main line including the first material web can be run. Although both the main line including the first material web and the auxiliary line including the second material web can be run at constant speed, the provision of an inventive apparatus with guide means which are arranged at an angle such that either the first and/or the second material web has a component of movement in the same direction as the direction of transport of the other material web, results in a lower or even zero relative velocity between the two webs. Thus, a processing step at the crossing point of the two webs can be carried out by simple means and without complicated and time-consuming procedures.
In accordance with a preferred apparatus with crossing first and second material webs as described above, the upstream and downstream guide means of the first material web are arranged at such an angle that there is periodically a zero or almost zero relative velocity of the first material web with respect to the second material web. Thus, by adjusting the angle at which the upstream and downstream guide means cross the principle direction of transport of the first material web, the change in direction of the first material web combined with the sinusoidal-like variation in the speed thereof produces varied speed components of the first material web in the longitudinal and lateral or transverse directions which can be maximized to coincide such that a zero relative speed between the first material web and the crossing second material web can be produced.
In another preferred embodiment of the apparatus having crossing first and second material webs, an inventive apparatus having transport means and guide means for producing a sinusoidal-like variation in the speed of the second material web can also be provided along the production line thereof. In this case, the intermediate position in the apparatus for varying the speed of the first material web and the intermediate position in the apparatus for varying the speed of the second material web overlap. Further, the upstream and downstream guide means of the second material web can also be arranged at an angle to the direction of transport of the second material web. Thus, by appropriately combining the effects of the guide means of both material webs and, optionally, the angles of the guide means to the principle direction of transport of the respective webs, the relative velocity between the crossing webs can be adjusted as desired to provide the optimal conditions for conducting the desired processing step at the crossing point.
The apparatus comprising crossing material webs as described above removes a possible bottle neck in a production line in which a product component which is best produced longitudinally needs to be mounted at an angle or transversely to the direction of movement of the main line. Furthermore, as desired, it is possible by way of the inventive apparatus with the crossing material webs to cross the auxiliary line including the second material web above or below the main line including the first material web. This provides the most options in terms of the design of the final product.